This invention relates to curable silicone compositions which provide high strength foams or elastomers. These foams or elastomers have high strength properties which are provided by a combination of organopolysiloxanes as the base polymer. The high strength properties are comparable to or better than the high strength properties of cured silicone compositions found in the art, but have the benefit of being less expensive to prepare.
Foamable compositions and curable elastomer forming compositions comprising a curable liquid hydroxyl-containing polyorgansiloxane base polymer, an organohydrogensiloxane crosslinker, and a curing catalyst are well-known in the art. Foamable compositions are known for example from U.S. Pat. No. 3,923,705, which issued Dec. 2, 1975 to Smith, which discloses basic foam compositions and methods and U.S. Pat. No. 5,414,023, which issued on May 9, 1995 in the name of Loiselle, et al, wherein the inventors therein recite numerous citations of patent and journal literature containing such information.
Patents dealing with such curable elastomer forming compositions are U.S. Pat. No. 5,279,894, which issued on Jan. 18, 1994 to Hoffman, et al, in which there is additionally used low viscosity dimethylvinyl chain-stopped (i.e. "terminal end blocked") dimethyl polysiloxane and alumina trihydrate to provide non-flammable adhesive products. Hoffman also discloses the additional use of vinyl-containing resinous siloxanes to provide the adhesive properties.
A patent, U.S. Pat. No. 4,590,222, which issued May 20, 1986 to Bauman deals with a vinyl-containing base polymer, a silicon hydride-containing crosslinker, a silanol terminated polydimethylsiloxane and also uses a benzene soluble, vinyl-containing siloxane resin as a profoamer.
Additional patents which deal with curable elastomer forming materials include U.S. Pat. No. 4.487,906, which issued Dec. 11, 1984 to Kniege, et al.; Bauman; U.S. Pat. No. 5,011,865 which issued Apr. 30, 1991 to Johnson, and U.S. Pat. No. 5,162,397 which issued Nov. 10, 1992 to Descamps. These latter four patents are included for what they teach about prior art curable siloxane elastomer forming compositions, but are considered to be irrelevant to the improved compositions of the instant invention.
The most pertinent of the prior art known to the inventors herein is the U.S. Pat. No. 5,279,894 recited supra.
The '894 patent discloses the use of additional siloxane polymers in the composition of the curable elastomer forming compositions, namely, the use of a low viscosity dimethylvinyl chain-stopped dimethyl polysiloxane which allegedly is used as a diluent, and a "branched chain" polymer which is actually a resinous material used to achieve adhesiveness for the composition.
The latter material is often referred-to as "resin reinforced polymer". Such use however does not anticipate the invention disclosed herein, nor make the invention disclosed herein obvious, owing to fact that the so-called "branched chain" polymer is actually a resin and there are no base polymer resinous materials required in the instant invention and there is no suggestion in the '894 patent to combine the specific siloxane materials of the instant invention, in the combinations disclosed herein, to obtain the benefits indicated.
The elastomer forming compositions claimed herein provide high strength elastomers as is shown by increased tensile strength, durometer and modulus, while holding the tear strength relatively constant, while in the foamed materials, higher strength foams can be prepared as is shown by tensile and tear measurements.